Stringent environmental regulations on chemical emissions and concern for worker exposure to chemicals have intensified the effort to eliminate emissions and minimize physical contact with sensitive materials. There is also a similar desire to limit exposure of consumers to aggressive and corrosive chemicals from a public health perspective. One approach to minimize this exposure during handling of chemicals is the use of pre-packaged unit doses using water-soluble packaging materials. Applications for unit dose packaging are convenient and limit the exposure of the user to different types of chemicals (such as laundry, dishwater or other detergents, pesticides, agriculture chemicals, bleaches, and the like). Presently, partially hydrolyzed polyvinylalcohol (PVA) is used for a number of these applications. However, PVA has limited chemical resistance and thermal stability and is not amenable to film formation by melt extrusion processes such as film casting from melt or blown film extrusion. A combination of moisture and elevated temperatures or the presence of acids and bases can catalyze the hydrolysis of the acetate groups which results in reduced solubility in cold water. For the same reason PVA also has poor shelf life and its solubility in water is adversely affected by storage time and conditions. There is a need for a polymeric composition that is consistently water-soluble to suit these applications.
Water-soluble polymers are either natural (biopolymers) or man-made. To be water-soluble these polymers are highly polar in nature. A large number of functional groups are used to impart polarity and, in turn, water-solubility to various polymers. Functional groups such as amines, hydroxyl, sulfonic acids, and carboxylic acids and their salts are commonly used to solubilize polymers. However, it is not uncommon for the reactive functional groups such as acids and amines to react with other acids and bases that they come in contact with during end-use, and this leads to changes in properties such as solubility. For an extensive review of this subject see “Water-Soluble Polymers”, Encyclopedia of Polymer Science & Engineering, Volume 17, pages 730–784, Second Edition, John Wiley & Sons (1989).
There is a long-felt need in the field for the development of a polyamide-based composition for such applications. Nylons are well known for their strength, toughness, abrasion resistance, lubricity, and chemical resistance. The use of nylons in basic packaging applications is widespread because of the aforementioned properties. See generally, Kohan, M. I., “Nylon Plastics Handbook”, Hanser/Gardner Publications, Inc., 1995, pages 514, 540, & 568–569. However their adaptation towards applications requiring solubility in water to date has not been particularly effective.
The patent literature includes various teachings regarding water-soluble nylons. U.S. Pat. No. 4,895,660 describes water-soluble sulfonated aromatic polyamides and polyureas that are cross-linked tonically with multi-valent metals for membranes, coatings, and adhesives. Japanese Patent Application 56-93704 describes a photosensitive composition comprising a water-soluble polyamide containing sodium sulfonate groups, a polymerizable unsaturated compound, and a sensitizer for printing plate applications. Japanese Patent Application 98007903A claims the use of alcohol-water solutions of nylons commonly known as PA66, PA46, PA6, and PA12 with a water-soluble methoxymethylated nylon, and thiocyanate salts in alcohol-water solvent as wiper blade coatings to improve performance and durability of the blades. U.S. Pat. Nos. 4,323,639 and 5,688,632 are both directed to water-soluble copolyamides containing polyether segments of 150 to 1500 molecular weight. These polyether-amide segments are obtained from polyether diamines and aliphatic dicarboxylic acids. These water-soluble polyamides are used in conjunction with photopolymerizable compound and a photoinitiator for printing plate applications.
It is well known in organic chemistry that ethers are relatively chemically unreactive compared to functionalities such as acids, amines, and hydroxyls. A water-soluble polyamide containing polyoxyethylene segments for water solubility would possess chemical inertness and thermal stability. These two characteristics would be advantageous in shaped-article production such as extrusion, blow-molding, and injection molding operations. However, up to now there has been no report in the literature on the use of water-soluble nylons containing polyoxycthylene segments for packaging and container applications and as a polymeric binder for tablets and briquettes.
It is an object of the present invention to provide a water-soluble nylon that can be incorporated into unit-dose packaging applications containing any of a variety of materials. It is a further object of the present invention to provide such materials that retain their integrity under ambient conditions and when immersed in water predictably solubilize and thereby release the contained material into aqueous solution. A feature of the present invention is its utility both as a packaging material (as envelopes, pouches and the like) and as a binder (for tablets, briquettes and the like). It is an advantage of the present invention that chemicals suitably packaged with materials described herein are not placed in contact with or only minimally contact persons handling the packaging. A further advantage of the present invention is its suitability for any of a number of conventional molding applications, including blow molding. These and other objects, features and advantages of the present invention will become better understood upon having reference to the description of the invention herein.